Missile firing weapons for example mortars have been utilized in warfare for many years. Mortars are traditionally under the direct control of field commanders and provide support generally unavailable from artillery or air support.
In modern warfare, traditional mortar techniques are inappropriate because the procedures utilized for aiming mortars indicate the location of the mortar and make it vulnerable to enemy fire. Such present procedures provide for a forward observer who selects targets and communicates the location to a mortar team which includes personnel who go in front of the mortar to place aiming stakes, where in placing the aiming stakes the personnel are many times subject to enemy fire.
The aiming device of a mortar generally comprises a sighting apparatus fixed on a mount connected to the mortar barrel by releasing means, a reference or aiming mark disposed at a certain distance from the mortar and suitable control means for the mount whereby the mortar is aimed.
In general, the mortar is put in an initial direction termed an observation or datum direction determined, for example, by means of two suitably spaced aiming posts. In order to aim the mortar, the deflection drum of the sighting apparatus is turned so that the plane containing the axis of the aiming telescopic sight and the axis of rotation of the deflection drum is parallel with the axis of the mortar barrel, the horizontality control device of the mortar is actuated to bring the bubble of the transverse spirit level between reference marks and the biped mount is moved by pivoting the mortar barrel in the socket or seat of the base-plate on which the rear end of the barrel rests, until the center of the cross wires of the sight of the sighting apparatus is in alignment with the aiming-posts determining the observation direction.
If it is required to effect a fire switch through a given angle, that is, to change the direction of fire, for example through a certain angle toward the right, the known procedure is adopted in pivoting the deflection drum through the same angle toward the left and thereafter pivoting the mortar barrel toward the right until the center of the cross-wires of the sight is once more on the aiming-post.
But if this post is not at infinity, that is, if the new line of sight is not parallel with the previous line of sight, the angle through which the barrel turns is less than the desired angle. The difference is greater as the aiming-post is nearer the mortar, since it is only when this post is at infinity that the new line of sight is parallel with the previous line of sight and that the desired fire switch is obtained.
Now, in practice, it is sometimes necessary to fire from a defiladed position (cave, shell hole, etc.) which does not permit an aiming mark to be placed at a sufficient distance (about 50 meters) to suitably reduce the aiming error in azimuth because the aiming mark is not at infinity (parallax error).
If the aiming mark can only be positioned at a lesser distance from the mortar, for example, at 1.5 meters from the socket of the base plate, it is practically impossible to fire with sufficient accuracy in using a conventional aiming device notably in the case of firing in any direction in azimuth.
Moreover, present procedures require exercise time in setting up the mortar position and aiming so that mobility is sacrificed. These arrangements for aiming mortars have been developed as shown in U.S. Pat. No. 2,977,858 and my U.S. Pat. No. 4,062,190.